docs: def select_lamb(self, lamb=None, out=bool):
          """ Return a wavelength index array
  
          Return a boolean or integer index array, hereafter called 'ind'
          The array refers to the reference time vector self.ddataRef['lamb']
  
          Parameters
          ----------
          lamb :     None / float / np.ndarray / list / tuple
              The time values to be selected:
                  - None : ind matches all wavelength values
                  - float : ind is True only for the wavelength closest to lamb
                  - np.ndarray : ind True only for the wavelength closest to lamb
                  - list (len()==2): ind True for wavelength in [lamb[0],lamb[1]]
                  - tuple (len()==2): ind True for wavelength outside ]t[0];t[1][
          out :   type
              Specifies the type of the output index array:
                  - bool : return a boolean array of shape (self.ddataRef['nlamb'],)
                  - int : return the array as integers indices
  
          Return
          ------
          ind :   np.ndarray
              The array of indices, of dtype specified by keywordarg out
  
          """
          if not self._isSpectral():
              msg = ""
              raise Exception(msg)
          assert out in [bool,int]
          ind = _select_ind(lamb, self._ddataRef['lamb'], self._ddataRef['nlamb'])
          if out is int:
              ind = ind.nonzero()[0]
          return ind